The present invention relates to a video tape recorder and more particularly to apparatus for selectively recording and reproducing a digital video signal which provides smooth continuation in the video picture reproduced from a medium on which new digital video signals are recorded immediately following previously recorded digital video signals.
Digital video tape recorders are known to convert an analog video signal into a digital video signal and then record the digital video signal on a magnetic tape medium. The recording and reproducing of digital video signals is more advantageous than the recording and reproducing of analog video signals because the picture quality of the reproduced digital video signal will not deteriorate through multiple dubbings. Moreover, error correction by way of digital processing further minimizes distortion of the reproduced digital video signal.
However, when an analog video signal is digitized, the amount of data representing that video signal is substantially greater than its analog counterpart. For this reason, data compression which uses a technique known as segment-recording typically is used to record the digital video signal. Segment-recording refers to recording one field interval of a digital video signal on a plurality of tracks.
One type of video tape recorder using the segment-recording technique utilizes several magnetic heads on a rotary drum, with each magnetic head recording a portion of a field interval of the digital video signal. In one embodiment, a plurality of magnetic heads scan tracks simultaneously resulting in an arrangement wherein the number of heads mounted on the rotary drum is significantly greater than traditional analog video tape recorders and this leads to the disadvantage that the construction of the rotary drum becomes complicated. When the mode of operation is switched from a reproducing mode to a recording mode in a video tape recorder using the segment-recording technique as described above, mode switching must occur in synchronization with the rotation of the rotary drum to provide smooth continuation in the recorded picture.
Another type of video tape recorder using the segment-recording technique includes a rotary drum having an arrangement of magnetic heads similar to that of an analog video recorder, but wherein the rotating speed of the rotary drum is increased such that a field interval is recorded on a plurality of tracks during the time period of one field. However, this type of video tape recorder may not provide a smooth continuation in the recorded video picture when switching from a reproducing mode to a recording mode since there is a high probability that such switching will not occur at the end of a field interval. For example, at the changeover point, reproduction of the digital video signal will terminate at a point when some but not all of the tracks included in one field interval are reproduced, but recording which starts at the beginning of a field is then initiated at a point located somewhere in the middle of this field interval thus resulting in a distorted transition from the signal which had previously been recorded to the signal presently being recorded.
Furthermore, a digital video signal derived from or representing a "standard" television signal and a digital video signal derived from or representing a high definition television signal may be recorded by the same video recorder. (For the purpose of the present discussion, and as used herein, a "standard" television signal is a television signal that conforms to a conventional broadcast format, such as NTSC, PAL, SECAM or the like.) The number of tracks necessary to record a field interval of a digital video signal representing a standard television signal is different from the number of tracks necessary to record a field interval of a digital video signal representing a high definition television signal. Therefore, the video tape recorder of the above design must have two different rotating speeds of the rotary drum in order to record and reproduce digital video signals representing standard and high definition television signals. However, smooth continuation of the video picture is difficult to achieve at the changeovers of reproduction and recording of these digital video signals for the above noted reasons.